(emacs)Select Tag Table

Selecting a Tag Table
---------------------
Emacs has at any time one "selected" tag table, and all the commands
for working with tag tables use the selected one. To select a tag
table, type `M-x visit-tags-table', which reads the tag table file name
as an argument. The name `TAGS' in the default directory is used as the
default file name.
All this command does is store the file name in the variable
`tags-file-name'. Emacs does not actually read in the tag table
contents until you try to use them. Setting this variable yourself is
just as good as using `visit-tags-table'. The variable's initial value
is `nil'; that value tells all the commands for working with tag tables
that they must ask for a tag table file name to use.
Using `visit-tags-table' to load a new tag table does not discard
the other tables previously loaded. The other tags commands use all
the tag tables that are loaded; the first one they use is the one that
mentions the current visited file.
You can specify a precise list of tag tables by setting the variable
`tags-table-list' to a list of strings, like this:
(setq tags-table-list
'("~/emacs" "/usr/local/lib/emacs/src"))
This tells the tags commands to look at the `TAGS' files in your
`~/emacs' directory and in the `/usr/local/lib/emacs/src' directory.
The order depends on which file you are in and which tags table
mentions that file, as explained above.